# Wave propagation # Paraxial approximation Under the [[Paraxial approximation]] we model a thick lens as a pair of [Optical Interfaces](Optical%20Interface.md) where we account for the ray transformation at the input, through the material, and then at the output. If the interior of the lens is completely homogeneous then propagation through the lens itself is modeled as a [free space propagation](Free%20space%20light%20propagation.md). ## ABCD matrix #Electromagnetism/Optics #ExperimentalTools/ExperimentalToolsinOptics